U.S. patent application number 11/175865 was filed with the patent office on 2006-01-12 for sensor head of reflective optical encoder.
This patent application is currently assigned to OLYMPUS CORPORATION. Invention is credited to Takeshi Ito.
Application Number | 20060007451 11/175865 |
Document ID | / |
Family ID | 35149300 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060007451 |
Kind Code |
A1 |
Ito; Takeshi |
January 12, 2006 |
Sensor head of reflective optical encoder
Abstract
A sensor head in a reflective optical encoder has a light source
that projects a light beam to be applied to a scale, and two
semiconductor substrates. The semiconductor substrates respectively
have photodetectors that detect the light beam reflected and
modulated by an optical pattern of the scale and electrical pads
that are configured to be connected to an external circuit, and at
least one of the semiconductor substrates has an electrical circuit
that processes signals output from the photodetectors. The sensor
head also has electric wiring lines that electrically connect the
electrical pads of the two semiconductor substrates, and a package
that contains the light source and semiconductor substrates.
Inventors: |
Ito; Takeshi; (Hino-shi,
JP) |
Correspondence
Address: |
Scully, Scott, Murphy & Presser
400 Garden City Plaza
Garden City
NY
11530-3319
US
|
Assignee: |
OLYMPUS CORPORATION
TOKYO
JP
|
Family ID: |
35149300 |
Appl. No.: |
11/175865 |
Filed: |
July 6, 2005 |
Current U.S.
Class: |
356/616 |
Current CPC
Class: |
G01D 5/366 20130101;
G01D 5/34715 20130101 |
Class at
Publication: |
356/616 |
International
Class: |
G01B 11/14 20060101
G01B011/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2004 |
JP |
2004-203753 |
Claims
1. A sensor head that is combined with a scale having an optical
pattern to constitute a reflective optical encoder comprising: a
light source that projects a light beam to be applied to the scale;
two semiconductor substrates that respectively have photodetectors
that detect the light beam reflected and modulated by the optical
pattern of the scale and electrical pads that are configured to be
connected to an external circuit, at least one of the two
semiconductor substrates having an electrical circuit that
processes signals output from the photodetectors; electric wiring
lines that electrically connect the electrical pads of the two
semiconductor substrates; and a package that contains the light
source and semiconductor substrates.
2. A head according to claim 1, wherein the electric wiring lines
include an electric wiring line that transmits a signal a signal
from one of the photodetectors on the two semiconductor substrates
to the electrical circuit on the other semiconductor substrate.
3. A head according to claim 1, wherein the two semiconductor
substrates respectively have electrical circuits that respectively
process the signals output from the photodetectors.
4. A head according to claim 3, wherein the electric wiring lines
include an electric wiring line that allows to be shared a
reference signal for the electrical circuits on the semiconductor
substrates.
5. A head according to claim 3, wherein one of the photodetectors
comprises a moving amount detection photodetector that detects a
signal in accordance with movement of the scale, the two
semiconductor substrates comprise a first semiconductor substrate
that has the moving amount detection photodetector and a second
semiconductor substrate, an electrical circuit of the first
semiconductor substrate includes an analog circuit that processes a
current signal output from the moving amount detection
photodetector to output an analog signal, and an electrical circuit
of the second semiconductor substrate includes a pulse circuit that
pulses the analog signal to output a digital signal.
6. A head according to claim 3, wherein one of the photodetectors
comprises a moving amount detection photodetector that detects a
signal in accordance with movement of the scale, the two
semiconductor substrates comprise a first semiconductor substrate
that has the moving amount detection photodetector and a second
semiconductor substrate, an electrical circuit of the first
semiconductor substrate includes an analog circuit that processes a
current signal output from the moving amount detection
photodetector to output an analog signal, and an electrical circuit
of the second semiconductor substrate includes a interpolator that
interpolates the analog signal.
7. A head according to claim 3, wherein one of the photodetectors
comprises a moving amount detection photodetector that detects a
signal in accordance with movement of the scale, the two
semiconductor substrates comprise a first semiconductor substrate
that has the moving amount detection photodetector and a second
semiconductor substrate, an electrical circuit of the first
semiconductor substrate includes an analog circuit that processes a
current signal output from the moving amount detection
photodetector to output an analog signal, and an electrical circuit
of the second semiconductor substrate includes a pulse circuit that
pulses the analog signal to output a digital signal and a
interpolator that interpolates the analog signal.
8. A head according to claim 3, wherein the two semiconductor
substrates comprise a first semiconductor substrate and a second
semiconductor substrate, the photodetector on the first
semiconductor substrate comprises a moving amount detection
photodetector that detects a signal in accordance with movement of
the scale, and the photodetector on the second semiconductor
substrate comprises a reference position detection photodetector
that detects a signal in accordance with a reference position of
the scale.
9. A head according to claim 8, wherein the electrical circuit of
the first semiconductor substrate includes a first analog circuit
that processes a periodic signal output from the moving amount
detection photodetector, and the electrical circuit of the second
semiconductor substrate includes a second analog circuit that
processes the reference position signal output from the reference
position detection photodetector and a pulse circuit that pulses
the periodic signal output from the first analog circuit.
10. A head according to claim 8, wherein the electrical circuit of
the first semiconductor substrate includes a first analog circuit
that processes a periodic signal output from the moving amount
detection photodetector, and the electrical circuit of the second
semiconductor substrate includes a second analog circuit that
processes the reference position signal output from the reference
position detection photodetector and a interpolator that
interpolates the periodic signal output from the first analog
circuit.
11. A head according to claim 8, wherein the electrical circuit of
the first semiconductor substrate includes a first analog circuit
that processes a periodic signal output from the moving amount
detection photodetector, and the electrical circuit of the second
semiconductor substrate includes a second analog circuit that
processes the reference position signal output from the reference
position detection photodetector, a pulse circuit that pulses the
periodic signal output from the first analog circuit, and a
interpolator that interpolates the periodic signal output from the
first analog circuit.
12. A head according to claim 3, wherein the two semiconductor
substrates respectively have ground terminals and power supply
terminals that drive the electrical circuit, the package has
terminals configured to be connected to an external circuit, and
the electric wiring lines have an electric wiring line that
electrically connects the power supply terminals in the package and
an electric wiring line that electrically connects the ground
terminals in the package, the electric wiring line that connects
the power supply terminals and the electric wiring line that
connects the ground terminals being connected to the terminals of
the package that is configured to be connected to the external
circuit.
13. A head according to claim 8, wherein the two semiconductor
substrates are arranged on two sides of the light source in a
direction substantially perpendicular to a moving direction of the
scale.
14. A head according to claim 3, wherein the package has a box-like
housing and a lid member having a light-transmitting portion, the
light source is fixed to the housing, the semiconductor substrates
are fixed to the lid member, and at least some of the electric
wiring lines are formed on the lid member.
15. A head according to claim 3, further comprising a slit on an
optical path along which the light beam projected from the light
source is directed to the scale.
16. A head according to claim 3, wherein at least one of the
electric wiring lines is not exposed to an outside of the
package.
17. A sensor head that is combined with a scale having an optical
pattern to constitute a reflective optical encoder comprising: a
light source for projecting a light beam to be applied to the
scale; two semiconductor substrates each having a photodetector for
detecting the light beam reflected and modulated by the optical
pattern of the scale and electrical pads for connecting an external
circuit, at least one of the two semiconductor substrates having an
electrical circuit for processing signals output from the
photodetectors; electric wiring lines electrically connecting the
electrical pads of the two semiconductor substrates; and a package
containing the light source and semiconductor substrates.
18. A head according to claim 17, wherein each of the two
semiconductor substrates has an electrical circuit for processing
the signal output from the photodetector thereon.
19. A head according to claim 18, wherein the two semiconductor
substrates comprise a first semiconductor substrate and a second
semiconductor substrate, the photodetector on the first
semiconductor substrate comprises a moving amount detection
photodetector for detecting a signal in accordance with movement of
the scale, and the photodetector on the second semiconductor
substrate comprises a reference position detection photodetector
for detecting a signal in accordance with a reference position of
the scale.
20. A head according to claim 19, wherein the two semiconductor
substrates are arranged on two sides of the light source in a
direction substantially perpendicular to a moving direction of the
scale.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2004-203753, filed Jul. 9, 2004, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical encoder.
[0004] 2. Description of the Related Art
[0005] Currently, so-called encoders such as optical and magnetic
encoders have been used to detect displacement amounts in a linear
direction for machine tool stages, three-dimensional measurement
instruments, and the like, and to detect rotational angles for
servo motors and the like.
[0006] An optical encoder generally comprises a scale fixed to a
displacement measurement target such as a stage and a sensor head
to detect the displacement of the scale. The scale has a movement
detection pattern whose optical characteristics change periodically
in the moving direction. The sensor head has a light-emitting unit
to apply a light beam to the scale and a detector to detect the
light beam modulated by the scale. The moving amount of the scale
is calculated on the basis of a change in intensity of the light
beam detected by the detector.
[0007] An optical encoder has characteristics such as high
precision, high resolution, noncontact, and high electromagnetic
interference resistance, and hence is used in various fields. As
encoders demanding high precision and high resolution, in
particular, optical encoders are most popular.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention is directed to a sensor head that is
combined with a scale having an optical pattern to constitute a
reflective optical encoder. The sensor head according to the
present invention has a light source that projects a light beam to
be applied to the scale, and two semiconductor substrates. The
semiconductor substrates respectively have photodetectors that
detect the light beam reflected and modulated by the optical
pattern of the scale and electrical pads that are configured to be
connected to an external circuit, and at least one of the
semiconductor substrates has an electrical circuit that processes
signals output from the photodetectors. The sensor head also has
electric wiring lines that electrically connect the electrical pads
of the two semiconductor substrates and a package that contains the
light source and semiconductor substrates.
[0009] Advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention.
Advantages of the invention may be realized and obtained by means
of the instrumentalities and combinations particularly pointed out
hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0010] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the general description given
above and the detailed description of the embodiments given below,
serve to explain the principles of the invention.
[0011] FIG. 1 shows a reflective optical encoder according to the
first embodiment of the present invention;
[0012] FIG. 2 is a sectional view taken along the line II-II of the
reflective optical encoder shown in FIG. 1;
[0013] FIG. 3 is a view, seen from the scale side, of the sensor
head of the reflective encoder shown in FIG. 1;
[0014] FIG. 4 shows the circuit configuration of the sensor head
shown in FIG. 3;
[0015] FIG. 5 is a plan view of the scale shown in FIG. 1;
[0016] FIG. 6 shows an A-phase signal, B-phase signal, and Z-phase
signal detected by the sensor head;
[0017] FIG. 7 shows different electric wiring lines that may be
employed in place of the electric wiring lines shown in FIG. 4;
[0018] FIG. 8 shows the concept of the basic arrangement of a
transmissive optical encoder that uses a Talbot image;
[0019] FIG. 9 shows another light source using an LED that may be
employed in place of, e.g., the light source shown in FIG. 3;
[0020] FIG. 10 is a perspective view of a sensor head in a
reflective optical encoder according to the second embodiment of
the present invention;
[0021] FIG. 11 is a sectional view of the reflective optical
encoder including the sensor head shown in FIG. 10;
[0022] FIG. 12 is a plan view, seen from the scale side, of the
sensor head shown in FIG. 10;
[0023] FIG. 13 is a sectional view of a sensor head in a reflective
optical encoder according to the third embodiment of the present
invention;
[0024] FIG. 14 is a plan view, seen from the scale side, of the
sensor head shown in FIG. 13; and
[0025] FIG. 15 is a plan view, seen from the scale side, of a
portion of a sensor head according to a modification of the third
embodiment, the portion including a transparent member and
semiconductor substrates.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Embodiments of the present invention will be described below
with reference to the views of the accompanying drawing.
First Embodiment
[0027] FIG. 1 shows a reflective optical encoder according to the
first embodiment of the present invention. As shown in FIG. 1, the
reflective optical encoder comprises a scale 110 and a sensor head
120. The scale 110 is attached to a movement detection target,
which can move relative to the sensor head 120. The sensor head 120
detects the movement of the scale 110. The scale 110 can move with
respect to the sensor head 120 in directions of arrows.
[0028] As shown in FIG. 5, the scale 110 has two types of optical
patterns, i.e., a movement detection pattern 111 and a reference
position detection pattern 112. The movement detection pattern 111
and reference position detection pattern 112 are respectively
formed on two tracks that extend adjacent to each other in the
moving direction. The movement detection pattern 111 has a periodic
structure in the moving direction. The reference position detection
pattern 112 is provided at one portion in the moving direction.
[0029] The sensor head 120 comprises a light source 121 for
projecting a light beam to be applied to the scale 110, two
semiconductor substrates 141 and 142, and a package containing the
light source 121 and semiconductor substrates 141 and 142. The
package comprises a box-like housing 180 and a lid member 190
having a portion that transmits light. The lid member 190 is
attached to the housing 180 to close the opening of the housing
180. The housing 180 has electrode terminals 182 that are
configured to be connected to an external circuit.
[0030] The semiconductor substrate 141 has a moving amount
detection photodetector 131 for detecting the light beam reflected
and modulated by the movement detection pattern 111 of the scale
110. The semiconductor substrate 142 has a reference position
detection photodetector 132 for detecting the light beam reflected
and modulated by the reference position detection pattern 112 of
the scale 110.
[0031] FIG. 2 is a sectional view taken along the line II-II of the
reflective optical encoder shown in FIG. 1. As shown in FIG. 2, the
light source 121 is fixed to the housing 180. The semiconductor
substrates 141 and 142 are fixed to the lid member 190 by, e.g.,
flip-chip bonding.
[0032] FIG. 3 is a view, seen from the scale side, of the sensor
head of the reflective encoder shown in FIG. 1. As shown in FIG. 3,
the semiconductor substrates 141 and 142 having the moving amount
detection photodetectors 131 and 132, respectively, are arranged on
the two sides of the light source 121 in a direction substantially
perpendicular to the moving direction of the scale 110. The
semiconductor substrate 141 is provided with an electrical circuit
171 on a part of its region excluding the moving amount detection
photodetector 131. The semiconductor substrate 142 is provided with
an electrical circuit 172 on a part of its region excluding the
reference position detection photodetector 132. The electrical
circuits 171 and 172 on the semiconductor substrates 141 and 142
are electrically connected to each other through electric wiring
lines 151 and 152.
[0033] FIG. 4 shows the circuit configuration of the sensor head
shown in FIG. 3. As shown in FIG. 4, the electrical circuit 171 on
the semiconductor substrate 141 includes an I/V converting circuit
173 that I/V-converts a photocurrent output from the moving amount
detection photodetector 131 and a light source driving circuit 174
for driving the light source 121. The electrical circuit 172 on the
semiconductor substrate 142 includes an I/V converting circuit 177
that I/V-converts a photocurrent output from the reference position
detection photodetector 132, a digital circuit 175 that pulses the
I/V-converted analog signal, and an interpolator 176 that
interporates a periodical analog signal accompanying the movement
of the scale 110 and outputs it as a pulse.
[0034] These electrical circuits are arranged considering their
characteristics.
[0035] It is not preferable to transmit output signals from the
moving amount detection photodetector 131 and reference position
detection photodetector 132 to another semiconductor substrate as
photocurrents. This is because the photocurrents may be largely
influenced by noise from the connecting wiring lines. For this
reason, the I/V converting circuit 173 is formed on the
semiconductor substrate 141 that has the moving amount detection
photodetector 131. The I/V converting circuit 177 is formed on the
semiconductor substrate 142 that has the reference position
detection photodetector 132.
[0036] A moving amount detection signal output from the I/V
converting circuit 173 reflects the movement of the scale 110. A
reference position detection signal output from the I/V converting
circuit 177 reflects the presence/absence of the reference position
of the scale 110.
[0037] If these signals (the moving amount detection signal and
reference position detection signal) are superposed with noise from
the digital circuit 175 and interpolator 176, it appears as a sharp
change. In other words, the noise from the digital circuit 175 and
interpolator 176 causes a sharp change in the moving amount
detection signal and reference position detection signal. A similar
sharp change is also caused by the reciprocal movement of the scale
110 within a short period of time. In other words, the reciprocal
movement of the scale 110 within the short period of time also
causes a sharp change in the moving amount detection signal and
reference position detection signal.
[0038] In detection of the reference position, the reciprocal
movement of the scale 110 within a short period of time is not
significant. Accordingly, a sharp change in the reference position
detection signal may be neglected as noise. In detection of the
moving amount, the reciprocal movement of the scale 110 within a
short period of time is the information that should be detected.
Accordingly, a sharp change in the moving amount detection signal
cannot be neglected as noise.
[0039] In other words, the moving amount detection signal output
from the I/V converting circuit 173 is readily susceptible to noise
from the digital circuit 175 and interpolator 176. Therefore, the
I/V converting circuit 173 is desirably formed on a semiconductor
substrate that is different from the semiconductor substrate on
which the digital circuit 175 and interpolator 176 are formed. The
reference position detection signal output from the I/V converting
circuit 177 is not readily susceptible to noise from the digital
circuit 175 and interpolator 176. Therefore, if the I/V converting
circuit 177 is formed on the same semiconductor substrate on which
the digital circuit 175 and interpolator 176 are formed, it will
not cause much trouble.
[0040] For this reason, the digital circuit 175 and interpolator
176 are formed on the semiconductor substrate 142 that is different
from the semiconductor substrate 141 that has the I/V converting
circuit 173. The I/V converting circuit 177 is formed on the
semiconductor substrate 142 that has the digital circuit 175.
[0041] The light source driving circuit 174 is not likely to
generate noise and accordingly arranged on the semiconductor
substrate 141 that has the moving amount detection photodetector
131. The light source driving circuit 174, however, generates heat
and may negligibly influence the circuit characteristics depending
on the position where it is mounted. Therefore, the position to
mount the light source driving circuit 174 must be selected
carefully.
[0042] Referring back to FIG. 3, the electric wiring lines 151 and
152 are formed on that surface of the lid member 190 which faces
the semiconductor substrates 141 and 142. The two electrical
circuits 171 and 172 are electrically connected to each other
through the electric wiring lines 151 and 152. The electric wiring
lines 151 only connect the electrical circuits 171 and 172 and are
not exposed outside the package. The electric wiring lines 152 are
connected to the electrode terminals 182 formed on the housing 180
and configured to be connected to the external circuit. The
electrical circuits 171 and 172 are designed to be operated by the
same driving voltage Vcc. Hence, a ground voltage Vgnd and the
driving voltage Vcc from the external circuit are applied to the
electrode terminals 182 of the package. The electric wiring lines
152 from the electrode terminals 182 branch as the electric wiring
lines 152 shown in FIG. 3 and extend to the two electrical circuits
171 and 172.
[0043] The electric wiring lines formed on the lid member 190
include not only the electric wiring lines 151 that merely connect
the electrical circuits 171 and 172 and the electric wiring lines
152 that connect the electrical circuits 171 and 172 and are
configured to be connected to the external circuit through the
package but also electric wiring lines or the like that extend from
the electrical circuit 171 or the electrical circuit 172 or both,
as needed, to the package but not to the other one.
[0044] The operation of the reflective encoder will be
described.
[0045] Referring to FIG. 1, part of the light beam projected from
the light source 121 is reflected and modulated by the movement
detection pattern 111 on the scale 110 and enters the moving amount
detection photodetector 131. The intensity of the light beam
entering the moving amount detection photodetector 131 changes
periodically in accordance with the movement of the movement
detection pattern 111. Hence, the moving amount detection
photodetector 131 outputs a signal current that changes
substantially periodically in accordance with the movement of the
scale 110 to the I/V converting circuit 173 in the electrical
circuit 171. The I/V converting circuit 173 I/V-converts the input
signal current into a voltage signal. This voltage signal contains
periodical signals called A- and B-phase signals the phases of
which are different from each other by 90.degree., as shown in FIG.
6.
[0046] Part of the light beam projected from the light source 121
is applied to that track on the scale 110 which the reference
position detection pattern 112 is formed on. When the scale 110 is
at the reference position, the reference position detection pattern
112 is located on the optical path of the light beam. The light
beam reflected by the reference position detection pattern 112
enters the reference position detection photodetector 132. When the
scale 110 is not at the reference position, the reference position
detection pattern 112 is off the optical path of the light beam. A
very small quantity of light beam reflected by the surface of the
scale 110 enters the reference position detection photodetector
132. The reference position detection photodetector 132 outputs a
signal current that changes almost in a binary manner in accordance
with the presence/absence of the reference position detection
pattern 112 to the I/V converting circuit 177 in the electrical
circuit 172. The I/V converting circuit 177 I/V-converts the input
signal current into a voltage signal. This voltage signal is a
so-called Z-phase signal and shows a high output voltage, as shown
in FIG. 6, when the scale 110 is located near the reference
position. Therefore, whether or not the scale 110 is located at the
reference position can be determined on the basis of the Z-phase
signal.
[0047] The A- and B-phase signals output from the I/V converting
circuit 173 of the electrical circuit 171 are input to the digital
circuit 175 in the electrical circuit 172 through the electric
wiring lines 151 or 152 and converted into pulses. The Z-phase
signal output from the I/V converting circuit 177 in the electrical
circuit 172 is also input to the digital circuit 175 and
pulsed.
[0048] According to this embodiment, the electrical circuits to be
formed on the two semiconductor substrates 141 and 142 are
arbitrarily distributed between the empty regions of the two
semiconductor substrates 141 and 142 considering various respects,
e.g., the functions, roles, and circuit feature sizes of the
electrical circuits, and whether or not each circuit affects the
other electrical circuits as a noise source. With this arrangement,
the electrical circuits to be mounted on the semiconductor
substrates can be optimized, and the qualities of the electrical
circuits can be improved. More specifically, the I/V converting
circuit 173 outputs the moving amount detection signal that is
readily susceptible to the noise from the digital circuit 175 and
interpolator 176. The I/V converting circuit 173 is formed on the
semiconductor substrate 141 that is different from the
semiconductor substrate 142 that has the digital circuit 175 and
interpolator 176. This can minimize the influence on the I/V
converting circuit 173. Thus, a circuit configuration that is not
influenced by noise as a whole can be obtained.
[0049] The electrical circuits on the two semiconductor substrates
141 and 142 are connected in the package to decrease the number of
terminals that serve for connection with the external circuit,
e.g., a power supply.
[0050] Since the electrical circuits 171 and 172 on the
semiconductor substrates 141 and 142 are electrically connected to
each other through the electric wiring lines 151 and 152, the
electrical circuits 171 and 172 can share a reference current
generation circuit and reference voltage generation circuit. That
is, the electrical circuits 171 and 172 can share a reference
signal (e.g., a reference voltage or reference current). Therefore,
the circuit feature size can be decreased. One reference voltage
and one reference current can be shared by circuits so that stable
circuit operation can be expected.
[0051] From the above description, downsizing, cost reduction, and
high performance of the reflective optical encoder are enabled.
[0052] According to this embodiment, the sensor head 120 has the
two semiconductor substrates 141 and 142. The sensor head 120 may
further comprise another semiconductor substrate that has an
electrical circuit. The electrical circuit on this additional
semiconductor substrate may be electrically connected to the
electrical circuits 171 and 172 on the semiconductor substrates 141
and 142.
[0053] According to this embodiment, the electric wiring lines 151
and 152 that electrically connect the electrical circuits 171 and
172 on the semiconductor substrates 141 and 142 are wiring patterns
formed on the surface of the lid member 190, as shown in FIG. 3.
The electric wiring lines 151 and 152 may be of any type as far as
they can be connected in the package. For example, as shown in FIG.
7, desired terminals of the electrical circuits 171 and 172 may be
electrically connected to each other by using electric wiring lines
153 formed on the lid member 190 and electric wiring lines 154
formed on the housing 180. Furthermore, the electric wiring lines
154 may be formed in the housing 180.
[0054] According to this embodiment, the light beam that is
projected from the light source 121 and then directly reflected by
the scale 110 is detected. To further improve the performance, a
so-called Talbot image may be employed.
[0055] A Talbot image will be described. For the sake of
simplicity, the following description will be made on the
assumption of a transmissive encoder. However, the same argument
holds for a reflective encoder.
[0056] FIG. 8 shows the concept of the basic arrangement of a
transmissive optical encoder that uses a Talbot image. Referring to
FIG. 8, assume that z1 is the distance between the light source 121
and the movement detection pattern 111 of the scale 110, z2 is the
distance between the movement detection pattern 111 of the scale
110 and the moving amount detection photodetector 131, p1 is the
pitch of the scale pattern, and p2 is the pitch of a Talbot image
projected onto the light-receiving surface of the moving amount
detection photodetector 131.
[0057] When z1 and z2 satisfy the relation represented by the
following equation (1), a bright and dark pattern similar to the
scale pattern is known to be projected on the moving amount
detection photodetector 131. The bright and dark pattern is called
the Talbot image. (1/z1)+(1/z2)=.lamda./(k(p1).sup.2) (1) where
.lamda. is the wavelength of the light beam projected from the
light source 121, and k is an integer.
[0058] To form a Talbot image, the light source 121 must
substantially be a point light source. As a substantial point light
source, an edge emitting laser, surface-emitting laser, current
confinement type LED, or the like can be used.
[0059] As shown in FIG. 9, the light source 121 may comprise an
ordinary LED 122 in place of a substantial point light source. In
this case, a transparent plate 123 having a slit is arranged on the
optical path along which a light beam projected from the LED 122 is
directed to the scale 110. The slit may have a single aperture, or
apertures that are periodically arranged at a predetermined period.
With this arrangement, even with an ordinary LED having a short
coherence length, a bright and dark pattern similar to a scale
pattern, like a Talbot image, can be obtained. The slit may be
formed, with the same method as that for the electric wiring lines,
on that portion of the lid member 190 which is located on the
optical path along which the light beam projected from the LED 122
is directed to the scale.
[0060] The pitch of the Talbot image projected onto the moving
amount detection photodetector 131 can be calculated by the
following equation (2): p2=p1.times.(z1+z2)/z1 (2)
[0061] By using the Talbot image, a high-performance optical
encoder can be formed with a comparatively simple arrangement.
Second Embodiment
[0062] FIG. 10 is a perspective view of a sensor head in a
reflective optical encoder according to the second embodiment of
the present invention. FIG. 11 is a sectional view of the
reflective optical encoder including the sensor head shown in FIG.
10. The section of FIG. 11 corresponds to the section of FIG. 2.
FIG. 12 is a plan view, seen from the scale side, of the sensor
head shown in FIG. 10. Referring to FIGS. 10, 11, and 12, members
indicated by the same reference numerals as those shown in FIGS. 1
and 2 are similar members, and a detailed description thereof will
be omitted.
[0063] The basic arrangement and operation of the reflective
optical encoder of the second embodiment are similar to those of
the reflective optical encoder of the first embodiment. A
description will be made on portions that are different from their
equivalents in the first embodiment.
[0064] As shown in FIGS. 10 and 11, a light source 121 and
semiconductor substrates 141 and 142 are all fixed to a housing
180. The electrodes on the semiconductor substrates 141 and 142 are
electrically connected to the electrodes on the housing 180 through
bonding wires 155.
[0065] The housing 180 has a cavity to attach the light source 121,
and rest-shaped portions to attach the semiconductor substrates 141
and 142. As shown in FIG. 11, the light source 121, a moving amount
detection photodetector 131, and a reference position detection
photodetector 132 are arranged so that the upper end of the light
source 121 and the upper surfaces of the photodetectors 131 and 132
are substantially leveled with each other.
[0066] As shown in FIG. 12, two electrical circuits 171 and 172 are
electrically connected to each other through bonding wires 156. In
other words, the electric wiring lines that connect the two
electrical circuits 171 and 172 comprise the bonding wires 156.
[0067] With this arrangement, a compact, high-performance encoder
can be provided technically easily.
[0068] According to this embodiment, the electric wiring lines that
connect the two electrical circuits 171 and 172 are the bonding
wires 156. Alternatively, these electric wiring lines may be
electric wiring lines formed on the surface of or in the housing
180.
Third Embodiment
[0069] FIG. 13 is a sectional view of a sensor head in a reflective
optical encoder according to the third embodiment of the present
invention. FIG. 14 is a plan view, seen from the scale side, of the
sensor head shown in FIG. 13. The section of FIG. 13 corresponds to
the section of FIG. 2. Referring to FIGS. 13 and 14, members
indicated by the same reference numerals as those shown in FIGS. 1
and 2 are similar members, and a detailed description thereof will
be omitted.
[0070] The basic arrangement and operation of the reflective
optical encoder of the third embodiment are similar to those of the
reflective optical encoder of the second embodiment. A description
will be made on portions that are different from their equivalents
in the second embodiment.
[0071] As shown in FIG. 13, the sensor head of this embodiment has
a transparent member 160. The transparent member 160 is located
between a light source 121 and a lid member 190, and its two ends
are respectively supported by semiconductor substrates 141 and
142.
[0072] As shown in FIG. 14, the transparent member 160 comprises
electric wiring lines 151 on its surface that faces the
semiconductor substrates 141 and 142. The electric wiring lines 151
connect electrical circuits 171 and 172 to each other.
[0073] With this arrangement, wire bonding need not be performed
across the two semiconductor substrates 141 and 142, and
accordingly the electric wiring lines can be easily formed and
connected simultaneously.
[0074] In this embodiment, a slit may be formed in the transparent
member 160, and detection using a Talbot image, which is described
in the first embodiment, can be performed.
[0075] FIG. 15 is a plan view, seen from the scale side, of a
portion of a sensor head using a Talbot image, as a modification of
the third embodiment, including the transparent member 160 and
semiconductor substrate 141 and 142. According to this
modification, slit apertures 161 and 162 and a light-shielding
portion 163 are formed in the transparent member 160. The slit
apertures 161 and 162 are located on an optical path along which a
light beam projected from the light source 121 is directed to the
scale 110. No light-shielding portions but apertures are formed
above the moving amount detection photodetector 131 and reference
position detection photodetector 132.
[0076] With this arrangement, a Talbot image can be formed and
detected easily. Therefore, a compact, low-cost, and
higher-performance reflective optical encoder can be formed.
[0077] In all the embodiments described above, the photodetectors
on the semiconductor substrates 141 and 142 are respectively a
moving amount detection photodetector and reference position
detection photodetector. Alternatively, the both photodetectors may
be moving amount detection photodetectors, or photodetectors to
detect periodic patterns having different pitches as in, e.g., a
vernier absolute encoder.
[0078] In all the embodiments described above, by using an LED as
the light source 121, both the requirements of low cost and high
performance can be met. By using an RCLED (Resonant Cavity LED) or
SLD (Super Luminescent Diode) as the light source 121, due to its
further excellent coherency, the characteristics of the encoder can
be further improved. In addition, by using various types of light
sources such as a surface-emitting laser, edge emitting laser,
current confinement type LED, or the like, an encoder can be formed
in accordance with a purpose.
[0079] Although the embodiments of the present invention have been
descried with reference to the views of the accompanying drawing,
the present invention is not limited to these embodiments and may
be variously modified or changed within the spirit and scope of the
invention.
[0080] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *